This invention is related to high temperature electrochemical cells and more specifically to systems for testing the electrolyte of the electrochemical cell while it is in use.
The high temperature electrochemical cell which uses a solid electrolyte is disclosed in U.S. Pat. No. 3,400,054, issued to R. J. Ruka el al. This cell has many uses, many of which are explained in this patent. One popular use for this cell is to monitor the oxygen level of flue gas as an indication of the combustion efficiency of a boiler, incinerator, or other burner device.
As stated in the Ruka patent, the solid electrolyte can be made of a solution of oxides such as zirconium oxide and scandium oxide. Electrodes are attached to either side of the electrolyte. The cell is designed so that the electrolyte forms two isolated chambers, with an electrode on each side of the electrolyte. For purposes of monitoring the oxygen content in the flue gas, a reference gas containing a known concentration of oxygen, or air from the atmosphere, is placed in one chamber and samples from the flue gas are circulated through the other chamber. The electrolyte is then heated and a potential difference is produced between each electrode of the electrolyte. The value of the potential difference is indicative of the ratio of oxygen content in the two chambers. To obtain a reading indicating the amount of oxygen in the flue gas, the potential difference produced can be placed across a resistor in series with an ammeter in a measuring circuit to determine the current produced.
Under normal operating conditions at temperatures from 800.degree. to 1200.degree. C, the electrolyte will have a low resistance between 25 to 100 ohms. However, once the electrolyte or its electrodes start to deteriorate, the resistance in the cell rises and can greatly affect the value read by the ammeter. As a result, when the electrolyte or electrodes start to deteriorate, the process operator detects only a gain in oxygen level and does not realize that the electrolyte deterioration is actually changing the value. Obviously, this can lead to improper control of the burning process.
Therefore, it is desirable to have some system for monitoring the quality of the electrolyte and its electrodes continuously while the electrochemical cell is being used so that when an operator determines the oxygen content of the flue gas he also knows that this is the actual oxygen content and that the reading is not being affected by a defective electrolyte or electrode.